A number of different radio telecommunication systems are known. A radio telecommunications system provides mobility for the mobile stations, i.e. the mobile stations are typically enabled to move from a location to another. A mobile station may also roam from one network to another network, if the other network is compatible with the standard the given mobile station is adapted to and there is a roaming agreement between the operators of the two networks. A radio telecommunications network is a cellular network consisting of cells. The cell can be defined as a service area covered by one or several base transceiver stations (BTS) serving mobile stations (MS) or similar user equipment (UE) via a radio interface. Examples of the multiple access cellular radio networks include CDMA (Code Division Multiple Access) or WCDMA (Wide-band CDMA) or TDMA (Time Division Multiple Access) system or FDMA (Frequency Division Multiple Access) systems and hybrids thereof.
The radio network system is typically provided with radio resource management function that may be based on the received noise raise of the received radio signal. A function of the radio resource management is to continuously adjust the transmission power levels between a base (transceiver) station (BS) and a mobile station (MS) associated with said base station during an ongoing connection between the base station and the mobile station. This is done in order to provide a sufficient quality for the transmission in various conditions. To reduce power consumption and interference it is also preferred to keep the required transmission power levels as low as possible at the same time. By means of this it is possible to avoid “wasting” network resources and power resources, and to enable as great a number of mobile stations as possible to communicate simultaneously with the base station having only limited power resources. The power resources of the base station may be limited both in transmission (downlink) and receiving (uplink) directions.
One power control mechanism is based on power control (PC) commands transmitted between two stations to cause the other station to alter or adjust or change its transmission power. The PC commands can be transmitted e.g. in a WCDMA closed loop functioning between the base station and the mobile station. The closed loop PC (CLPC) commands can be sent both in the uplink (towards the base station) and in the downlink (towards the mobile station), whereafter the base station or the mobile station will process the received command and reduce/increase its transmission power accordingly. The power control between the stations, such as the closed loop PC, may be controlled by another power control command generated by a controller of the communication system. For example, in the currently proposed WCDMA system it is envisaged that an outer loop power control (OLPC) command generated by a radio network controller (RNC) of the WCDMA system will attempt to set the connection quality target of a physical connection between the base station BS and the mobile station MS to be such that a required FER (Frame Error Ratio) target or BER (Bit Error Ratio) target or any other similar target of the connection is met with a minimal connection quality target. The closed loop power control command is then adjusted at the base station in accordance with the outer loop power control command received from the controller. The connection quality target may sometimes be referred to as a connection setpoint.
The connection quality target or setpoint can be announced e.g. by means of so called Eb/No (Signal Energy/Noise) target or SIR (Signal to Interference Ratio) target or desired signal level target or a similar parameter indicating a quality measure which can be estimated for the connection. The relationship between the parameters is such that the connection quality target (e.g. the SIR target) has to be set such that the FER or the BER or similar parameter of the connection remains at an appropriate level. The actual connection quality value (e.g. SIR) is then controlled in accordance with the target value, and one or several of used connection parameters having influence to the quality of the connection should follow any changes in the target value. In most cases it is sufficient if the transmission power is increased/decreased in order to meet the target value. The idea behind the arrangement is that by increasing the connection quality target value the transmission power (or any other appropriate transmission parameter having an influence over the connection quality) will increase and thus the connection quality will increase and the FER will improve.
When more than one radio station communicate within a certain area, the radio stations may interfere each others radio connection. A form of this interference problem is known as adjacent channel interference (ACI). The interfering stations may be in communication with the network apparatus of the same network system and operator. The interfering mobile stations may also be in communication with different radio networks operated by different operators. The interfering networks may even be based on a different standards and/or principles of operation.
Although it may be possible to ease the problem caused by the simultaneous radio traffic between several stations by careful network planning, the amount and nature of interference caused by radio apparatus of other network systems is very difficult to predict and/or take into account beforehand. Despite the careful network planning, adjacent channel interference caused by radio stations of the same system may still occur e.g. due to increase in the radio traffic and/or in the number of users roaming within a cell of the radio network.
A specific problem with the adjacent channel interference may occur when an interfering mobile station comes close to a base station, especially when the uplink transmission power of the interfering mobile station is relatively high compared to the other mobile stations. Uplink received power can be filtered by various filter means and thereby it may be possible to reduce the effect of short time or narrowband interference. However this may prove to be difficult to accomplish and does not totally solve the interference problem. Although filter means may be employed in order to minimise and/or normalise the problems caused by the interfering mobile radio station, the filter means have only a limited adjacent channel interference protection, and the interfering station may still block useful signals from the other stations.
Additional or unexpected interference in the uplink direction may influence adversely the radio resource management, since the radio resource management is based on the relative received power in the uplink. In the uplink the noise raise relative to noise floor (i.e. the basic noise of the system) is determined, and this should not exceed a predefined target (for example, 6 dB).
The noise raise describes the ratio of the total interference power and the noise power in the dB-scale. The noise raise can be calculated as follows:
                                                        Noise_raise              =                                                                    Interference                    +                    Noise                                    Noise                                ⁢                                                                  ⁢                in                ⁢                                                                  ⁢                linear                ⁢                                                                  ⁢                scale                ⁢                                                                  ⁢                and                                                                                        Noise_raise              =                                                10                  ·                                                            log                      10                                        ⁡                                          (                                                                        Interference                          +                          Noise                                                Noise                                            )                                                                      ⁢                dB                ⁢                                                                  ⁢                in                ⁢                                                                  ⁢                dB                ⁢                                  -                                ⁢                scale                                                                                  (          1          )                ,                                  ⁢                  (          2          )                    
The noise floor is denoted by the Noise-term in above equations (1) and (2). Noise floor typically contains the thermal noise, noise figure and other noises, which are not in the interference. The noise raise value can be measured by a base station e.g. by subtracting the noise floor from the avarage total received power.
The additional interference may change the assumptions made during the network planning so that the noise floor is no longer constant, but may become increased. As a consequence to this, some network capacity may be lost because of the interference. The interference problem may last only for short periods of time, and the occurrence of interference is hard to predict. Therefore the various interference instances may generate different kinds of unexpected fluctuations into the network. The interference may also cause a station to be dropped from the cell. The station's sensitivity to drop from the cell depends on uplink and/or downlink powers. In addition, the pure interference based load control, admission control and packet scheduler algorithms may not always be applicable for all radio environments (e.g. in micro or pico cells). Therefore it may be advantageous to base the management of the uplink load on some other factor. The other factor should be selected such that it is less sensitive for the adjacent channel interference (ACI) problem than the above described solutions. In the event of a strong adjacent channel interference (ACT), the conventional interference based radio resource management may clear/drop even the whole cell because of one interfering station that causes the adjacent channel interference into that cell.